[14.01] New Views of Jupiter's Rings

J. A. Burns (Cornell University)

Jupiter's rings are the archetype of ethereal planetary
rings (very-low optical-depth bands containing micron-sized
"dust"). As a result of much improved observations by
Galileo (Ockert-Bell* -- most citations are et al. and
Icarus in press* or this meeting) and Keck (de Pater*), we
now understand the nature of such rings. The ring has three
components: a ~104 km-thick toroidal halo (1.4-1.7 RJ;
normal optical depth t = 10-6), a thin main ring (1.7-1.8
RJ; t = 10-6), and a pair of exterior gossamer rings
(1.8-3.5RJ; t = 10-7). The main ring has patchy (~20-30
percent) brightness. The ring is reddish and its particles
satisfy a -2.5 differential power-law size distribution.
Because particle lifetimes are brief, the rings must be
continually regenerated, by collisions into parent bodies,
which may be unseen or may be the known small ring-moons
(Thomas*, Simonelli). The gossamer ring seems to be
collisional ejecta derived from the ring-moons Amalthea and
Thebe, and evolving inward by Poynting-Robertson drag
(Burns). The particles drift through many electromagnetic
resonances, clustering around synchronous orbit, which
produce jumps in the particles' inclinations (Hamilton). The
main ring is probably debris from Adrastea and Metis, which
orbit in the equatorial plane. The halo particles are driven
vertically by electromagnetic forces, which may be resonant
(Schaffer & Burns) or not (Horanyi & Cravens). When halo orbits
become highly distorted, particles are lost into Jupiter.
Similar faint rings may be attendant to all small, close-in
satellites (Showalter).